Oscillatory or transient responses of a servomechanism from whatever cause are obviously undesirable, and so it is necessary to provide some form of damping by which a load can be brought to rest in its required position with the minimum of overshoot. Varying degrees of damping can be applied. If there is too much extra viscous friction, the system is heavily damped and a very sluggish response is produced.
Critical damping:- The degree of damping which just prevents any overshoot is known as critical damping.
Optimum damping:- Damping which allows one small overshoot and gives the smallest settling time is known as optimum damping.
Light damping:- By inherent friction light damping is achieved.
Servomechanisms possess various inherent factors which, together, have the general effect of reducing the amplitude of each successive oscillation; such factors include
- static friction,
- kinetic friction,
- eddy current,
- lubricant viscosity, etc.,
While contributing to damping requirements they do have certain detrimental effects, e.g.
- power is wasted, and
- errors can be introduced with the servomechanism operating in the steady state.
The effects are partly due to a small force of constant magnitude known as coulomb friction, and to viscous friction which increases with speed.
